Process of oxidizing naphthenes



July 4 3933. H. o. FORREST ET AL.

PROCESS OF OXIDIZING NAPHTHENES Filed Jan. 31, 1930 2 Sheets-Sheet lJuly 4-, 1933. H O FORREST r AL 1,916,923

PROCESS OF OXIDIZING NAPHTHENES Filed Jami 51, 1950 2 Sheets-Sheet 2WlYNE$$E$ INVENTORJ 7k f 4 fwd Patented July 4, 1933 UNITED STATESPATENT OFFICE HENRY O. FORREST, OF ANDOVER, MASSACHUSETTS, AND PER. K.FROLICH, F ELIZA- BETH, NEW JERSEY, ASSIGNORS TO NATIONAL SYNTHETICCORPORATION, OF IPAINESVILLE, OHIO, A CORPORATION OF DELAWARE PROCESS OFOXIDIZING NAPHTHENES Application filed January 31, 1930. Serial No.424,905.

This invention relates to direct oxidation processes, and especially tothe partial oxidation of cyclic organic compounds.

The processes heretofore known and practiced for the commercialproduction or oxygenated aromatic or cyclic organic compounds are opento numerous objections.

' For example, in the prior liquid phase processes an active agent, suchas an alkali, a catalyst, has been necessary, or an intermediatecompound has been used, such as benzyl chloride in the production ofbenzoic acid from toluene, or else the necessary oxygen has beengenerated in a solution or suspension of the compound to be oxidized.Consequently it may be said that the prior liquid phase processes are ofan indirect naure, and are subject to the limitations of such processes.Thus, the use of auxiliary active agents and the like may cause lossesdue to side reactions and the use of a plurality of steps engendersdecreased yields, and the oxygenated product may be contaminated.Furthermore, the active agents and formation of intermediates add to thecost.

Vapor phase processes are of a more direct nature than those justreferred to, and because they are free from many of the disadvantages ofindirect processes, many vapor phase processes have been proposed andused for the oxidation of aromatic compounds to produce more usefulproducts. All oxidation processes, however, are exothermic, andconsequently there is a tendency toward complete degeneration to carbondioxide. To produce useful yields of a desired oxidation product thiseffect must be minimized by careful and accurate temperature control ofboth liquid and vapor phase processes. Such temperature control isparticularly difficult in vapor phase processes, because of the inherentdifficulty of regulating vapor temperatures, and because the processesunder consideration are all catalytic.

Vapor phase processes require the treatment of large volumes of gases,and even under the best conditions of operation it has not been possibleto maintain the entire body of gas in the reaction zone at a uniformtemperature. That is, although the gases at a.

heat-exchanging surface may be at proper temperature, the temperatureinwardly from the wall will be above optimum. Or if the center of thereaction zone is maintained at optimum temperature, the temperaturegradient is such that the gases at the wall are too cool. Consequently,the oxidation processes previously proposed for use with cyclic organiccompounds have been inefficient, the processes being attended by highcarbon dioxide formation, or by low conversion eificiencies. Also, it ischaracteristic of prior processes that the ring is usually broken withproduction of less valuable poducts.

In consequence of these and other disadvantages of the prior processesthere has been no completely satisfactory process available up to thepresent time for the commercial oxidation of cyclic organic compounds,all such processes being subject to the disadvantages referred to, andbeing also subject to the known diihculties and disadvantages which theuse of catalysts and other active agents present.

It is an object of this invention to provide a process for the partialoxidation of cyclic organic compounds, which effects direct oxi dationto the desired product, produces useful yields and minimizes sidereactions and complete degeneration to carbon dioxide, uses anoxygen-containing gas, preferably air, as the oxidizing medium isapplicable generally to the oxidation of compounds of the type referredto, is simple, efficient and readily controlled, and satisfactorilyovercomes many of the disadvantages of prior processes.

Among others it is a paratieular object to provide a process of the typereferred to in which active agents are not required, which makes use ofthe liquid phase, provides ready and accurate temperature control, doesnot require elaborate or unduly expensive apparatus, and which producesa maximum of products retaining a ring structure.

The accompanying drawings show two types of apparatus which may beusedin the practice of the invention, in which Fig. 1 is a schematicdrawing showing an apparatus adapted particularly for liquid phaseoperation; and Fig. 2 a vertical section through an apparatus adapted totwo-phase liquid-vapor operation.

The invention is primarily predicated upon our discovery that cyclicorganic compounds may be oxidized directly by molecular oxygen withoutthe intervention of actlve agents, by contacting them with oxygen in aclosed system at an elevated temperature and under a pressuresubstantially greater than the vapor pressure of the compound at thereaction temperature.

The invention is applicable to the oxidation of compounds of carbonhaving a closed ring structure, especially the aromatic and relatedcompounds, and an important feature is that the oxidation may becontrolled to prevent disruption of the ring, or to retain in theoxidized product at least one closed ring nucleus where the startingsubstance contains more than one ring. If benzene is treated inaccordance with the invention, the ring is broken, apparently becausethe splitting of an oxygen molecule in effecting oxidation of onehydrogen of the benzene ring leaves the other oxygen atom in such ahighly reactive state that it attacks another hydrogen atom, weakeningthe ring and causing its rupture. This untoward effect is apparentlyabsent or greatly repressed where one or more nuclear ydrogen atoms arereplaced by a side chain or other grou which is more readily oxidizedthan the hy rogen atoms attached to the nucleus. Accordingly, theinvention particularly contemplates the oxidation of (a) substitutedbenzene, or aromatic, compounds, and es cially the oxidation of purelyaliphatic si e chains attached to the nucleus, examples of such compoundbeing toluene and the xylenes, (b) polynuclear or condensed ringcompounds, for example naphthalene, and

0) naphthenes or hydroaromatic com ounds,

or example cyclohexane. All suc compounds are for brevity of referenceherein comprehended by the term cyclic organic compound.

Although the invention is especially applicable to the oxidation ofhydrocarbons of the type referred to it maybe applied to othersubstances, such as compounds initially containing oxygen, for example,cresols, aldehydes, and/or other cyclic organic c0m poun s. a

As previously stated, prior commercial processes have invariablyemployed a catalyst, an alkali, or oxygen-liberating or other auxiliarymaterials. All such substances are herein cojointly referred to asactive agents, and under the-invention as described none of them areessential.

In the practice of the invention the compound is treated with anoxygen-containing gas, and air will in most cases be whollysatisfactory. However, pure oxygen, ozone, and other oxygen-containinggases may be used.

In accordance with the invention, the total pressure in the system ismaintained at least at the vapor pressure of the reacting compound atthe temperature of the reaction, but preferably it is considerably inexcess of that value, and most suitably it is substantially in excess ofthe critical pressure of the compound. The reaction is carried out at anelevated temperature in excess of the melting point of the compoundbeing oxidized, and in the preferred practice it is above the normalboiling point of the compound but below that critical for the compound.

The temperature may be controlled in part by regulating theconcentration of oxygen with respect to that of the material undergoingoxidation, for example by admitting oxygen at such a rate with respectto the oxidizable substance that the heat evolved will not cause anexcessive temperature, or by dilution with an inert gas. However, in thecourse of our researches we have found that the temperature of highlyexothermic gasliquid reactions may be controlled readily to provideuniformity of temperature'throughout the reaction zone by vaporizing andcondensing in the s stem one or more components of its liqui phase, andthat this means is especially applicable to direct oxidations of thetvpe just referred to. In other words, the temperature of a gas-liquidreaction may be controlled directly by regulation of the total pressureon the system, as will be more fully explained hereinafter.

The invention may be practiced in various ways. For example, thematerial, liquefied if it is solid at normal temperatures, may betreated with an oxygen-containing gas, and when sufiicient gas has beendissolved in the liquid material, the liquid-gas solution is passedunder pressure into a reactor which has been preheated to a suitabletemperature. The liquid is preferably saturated with .oxygen to anamount sufficient to effect the desired oxidation.

This procedure may be practiced in connection with any suitableapparatus, for example that shown in Fig. 1. This ap aratus comprises asaturator 1 having an in ct conduit 2 provided with a branch 3 connectedto a source of oxygen-containing gas, such as an oxygen cylinder 4, anda branch 5 connected to a source of the compound to be oxidized, forexample a cylinder 6 containing toluene. The toluene or other materialmay be forced into the saturator by means of an inert gas, for ezxamplenitrogen, supplied through a plpe The liquid-gas solution is passedunder appropriate pressure through a conduit 8 into a pressure reactor 9supported in a heating bath 10, and in order to increase the exposureconduit 8 preferably terminates in a coil 11, most suitably of capillarytubing, disposed in the reactor. The solution may be forced through thereactor by means of a liquid trical heater, not shown.

The material forced through the reactor coil expands after leaving thereactor, and the products pass to a condensing system 14, wherecondensible substances are collected.

The residual gases are passed from the condensers through a conduit 15to a meter 16, and may be collected in a basometer for further use. Allof the lines are provided with suitable valves, as will be understood.

In the operation of this form of apparatus the compound or material tobe oxidized is contacted with molecular oxygen at an elevatedtemperature and under high pressure, and the reaction probably takesplace during passage of the compound through the reactor coil. Nocatalyst or other active agent is necessary, and our tests have shownthat the reaction is apparently not affected by the material of whichthe coil is composed, sev- 0 eral widely different metals having beenused for this purpose, which indicates that the reaction is one ofdirect oxidation by the molecular oxygen present.

The end products may be worked up in any 5 suitable manner, to separateand recover unreacted material and the oxidized product or products,such procedures being familiar chemical engineering unit processes. Theexit gases may contain carbon monoxide and/or dioxide and otherproducts, depending upon the type of gas initially used and the materialbeing treated, and where air has been used, they are generallyimpoverished of oxygen and rich in nitrogen. Such tail gases 5 may beworked up to recover desirable con stituents, or they may be used asinert pressure media in the process, any unnecessary excess beingdiscarded.

The temperature, pressure, gas concentra 0 tion, length of exposure toreaction conditions. etc. will vary according to the material beingtreated, the product desired, and the concentration of oxygen in thegas, and it is not possible to prescribe exact conditions for 5 allmaterials. However skilled workers may readily determine the conditionsfor any particular material, and they are further exemplified by thefollowing data selected from tests which we have made.

3 In these runs toluene was oxidized in an apparatus similar to thatjust described, pure oxygen under pressure being passed into thesaturator until the toluene had taken up an amount corresponding to thatshown in the 3 oxygen column of the following table. The

toluene-oxygen solution was then forced into the reactor, thetemperature in the reactor being maintained constant during the run.Calculations based on the time required for passage of the charge gavethe period during which one molecule of toluene remained in the reactor,this being given in the time column.

y Oxygen converted to Pres- Texn- Com- 53 sure, para 2%,? B

PM was. is s am am- ..a; C0.

% 1c acid hyde Toluene 4. 1 1000 270 25. 6 10. 5 13. 1 Toluene 4. l 1000305 30 24. 8 9. 9 5. 4 Toluene 4. 1 1000 300 2 26. 0 8. l 14. 0

It will be observed that in this series of tests the total usefulproducts are about the same at 270 C. as at 305 C., but that the carbondioxide formation is substantially less at higher temperatures.Furthermore, at a given temperature, no advantage is gained by longexposure to reaction conditions, the reaction apparently being veryrapid, as shown above as well as by other experiments which we havemade, in which substantially the same yields were obtained withexposures of about seconds. In these tests there was little, if any,carbon formation.

Adequate temperature control in the use of the apparatus just describedis effected by conduction of heat through the wall of the reaction tube.That is, the ratio of heat dissipating surface of the capillary coil tothe mass of reacting liquid within it is high. Also, the concentrationof oxygen with respect to the reacting liquid is low, and thiscombination of factors renders temperature control relatively easy insuch an apparatus.

The invention may also be practiced in other ways and in other apparatusthan those just described. For example, the oxidizing gas may be passedinto a large charge of the compound at reaction temperature in atwophase liquid-vapor system. In such operation, large amounts ofmaterial may react during any given interval, causing liberation oflarge amounts of heat, and accurate and uniform temperature controlthroughout the entire reaction zone is essential. In prior practice ofthis nature such exact control has not been accomplished, because of thedifficulty of attaining complete uniformity of temperature in thereaction mass even with the most modern heat exchanging systems. Ourinvention overcomes these difficulties and affords highly uniformtemperature control throughout the reaction zone.

As previously stated, the rate of reaction, and consequently the amountof heat liberated in unit time, may be regulated, to some extent atleast, by varying the concentration of oxygen with respect to thecompound undergoing oxidation, and one means of accomplishing this is bydilution of the oxygencontaining gas with an inert gas, for example byrecirculation of oxygen-impoverished effluent gases.

' A major feature of our invention, however, resides in our discoverythat almost perfect temperature control of exothermic gas-liquidreactions may be efi'ected by absorbing heat of reaction by evaporationof oneor more components of the liquid reaction charge and in heatingthe unreacted gases.

In thisembodiment, a charge of the material to be oxidized is placed ina closed reactor provided with refluxing means and with means forheating the charge, and a suitable oxygen-containing gas is passed intothe liquid charge. Due to the heat of reaction, the temperature of thematerial rises, and heat must be removed in order to maintain thereaction temperature. In accordance with this embodiment, use is made oflatent heats of evaporation of the reaction materials and the heatcapacity of the gases concerned for that purpose.

At any given temperature the liquid exerts a definite vapor pressure,and vaporization takes place. The amount of heat thus absorbed dependsupon the amount of vaporization taking place. Because vaporization takesplace into the inert or unconsumed fraction of the oxidizing gas, theamount of vaporization is in part controlled by the ratio of vaporpressure to total pressure. This ratio is determined by the temperatureand total pressure due to the vapor pressure of the reacting materialand the pressures exerted by the unconsumed fraction of the oxidizinggas, oxides of carbon, and other products of reaction. Therefore, byoperating at a suitable pressure the ratio of vapor to inert gas isregulated and the temperature of these liquid-gas reactions may beetfectivcly and accurately controlled. From what has been said, it willbe seen that this operating pressure is determined by the amount of heatto be removed by vaporization per mol. of inert gas.

The relation of the factors in this process may be shown by andunderstood from the following considerations. Considering first thesimplest case, it. is essential to have (1) an adiabatic system, (2) alloxygen reacting, (3) no gaseous or volatile products formed, (4)materials preheated to reaction temperature, and (5) equilibrium betweenliquid and vapor. If Q equals the heat evolved per mol. of oxygenreacting, n the number of mols. of material vaporized in absorbing thisheat, and V the molal heat of evaporation of the material at reactiontemperature, then Q=nV, and

If L represents the vapor pressure of the material, P the total pressurein the system,

and r the mols. of inert gas to mols. of oxygen, then and bysubstitution in this equation of the value of n from Equation I,

P=LM Eq. III.

With air as the oxidizing gas, this equation becomes Eq. II.

If the materials are pumped to the reactor cold, and assuming about percent of the heat to be used in preheating,

0.2 x 100000+ (3.76 x 6000) P 0.2 x 100000 Eq. IV.

P 400 490 pounds.

pounds.

In case the gas contains only 10 per cent of oxygen, per cent of theheat being consumed in preheating, the pressure would be P (O.15 311050(101(30-(|;80X 6000 1840 pounds.

Where air is used, 1' is fixed, and the pressure is determined by theheat to be removed.

Where heat losses from the system are high,

the pressure must be high, or too much liquid will be evaporatedand thesystem will operate at too low a. temperature. Where heat losses arelow, the pressure will still be above the vapor pressure of the reactingliquid. If the pressure is maintained at that required for desiredreaction temperature, the heat will be removed as rapidly as it isevolved, but if the pressure is too high, an insuflicient amount ofvapor will be removed per unit volume of oxygen and the temperature willrise until equilibrium is effected by vaporization. On the other hand,if the pressure maintained in the system is too low, an excessive amountof liquid will be evaporated, and the temperature of the material willbe below that desired.

Except for the assumption that no volatile products are formed, thefactors on which the development of the foregoing equations is based arejustified, because they can be substantially realized. Gaseous productswill generally be formed, however, and in this case, assuming X==mols.of volatile products per mol. of oxygen, S=mols. of material supplied tothe system, Tr=reaction temperature, Tg and Tl=entering temperature ofgas and material respectively, Cpg and Cpl= average molal heat capacityof gas and material, then Q=nV+ (Z+r) (T1'Tg) (Opg) d S(Tr-TZ) Cpl, an

and solving may be regulated so as to continue it by the heat ofoxidation, although the equations given show that heat input wouldpermit the pressure to be decreased to the vapor pressure of thecompound. However, for reasons of economy, such heat input isundesirable, and the minimum pressure will generally be con: siderablyabove the vapor pressure at the reaction temperature, the usefulpressures in most cases lying between about 750 and 2500 pounds persquare inch.

The process may be performed in batch or continuous fashion. In batchoperation, the reaction products may be withdrawn from connection 21. Inthe case of continuous oporation fresh compound may be continuouslyintroduced through inlet 21, and partially oxidized liquid withdrawn inequal amount from the reaction chamber, for example through an outletpipe 32. The reacted material thus withdrawn may be worked up forseparation of its products, from unreacted material, or it may bereturned directly to the system.

While the oxygen-containing gas may be introduced intermittently, tomaintain the proper oxygen concentration in the reactor, it is mostdesirable to introduce this gas continuously, and preferably atsubstantially the rate at which it is consumed.

from which the operating pressure for a given set of conditions may becalculated.

This modified procedure may be performed in various ways, one of whichmay be understood in connection with Fig. 2. The reactor shown comprisesa lower reaction chamber 20 provided with an inlet connection 21 forintroducing a charge 22 of material to be oxidized, and an upper refluxportion 23 having means for condensing vapors arising from the reactionzone. In the form shown, the condenser consists of an ordinary tubebasket 24 around the tubes of which cooling water may be circulated, asby means of inlet and discharge conduits 25 and 26. The chamber 20 isprovided with means for heating the charge, such as an electric heater27, and oxygen-containing gas is passed into the charge through an inletpipe 28, means such as a spreader dome 29 being preferably provided todistribute the gas throughout the charge. The apparatus is also providedwith a pressure-controlling valve 30 of any suitable type, preferablyone which is adJustable to automatically relieve the pressure at apredetermined value. A pressure gauge 31 is also provided.

In the use of this apparatus it Wlll usually be desirable to discontinueheatlng after the reaction has started, because the reactlon Tests whichwe have made of the modified procedure described above also demonstratethe benefits to be derived from the invention. In these tests, anapparatus embodying the constructional features shown in Fig. 2 wasused, and air was used as the oxygen-containing gas. In one run, toluenewas charged into the reactor and heated to 280 (1, this temperaturebeing maintained in the manner described by maintaining the totalpressure at 1000 pounds per square inch. The reaction liquid was cycledcontinuously, and air was passed into the liquid in the reactor at arate such that the inlet oxygen corresponded to 9.1 mol. per cent. Uponanalysis of the reaction mixture, it was found that the benzoic acid andbenzaldehyde concentrations were 3.3 and 1.0 per cent respectively,corresponding to oxygen conversions of 25.6 and 3.5 per centrespectively. The conversion of oxygen to carbon dioxide was 11.6 percent.

In a similar run, at 280 C., with inlet oxygen corresponding to 23.7mol. per cent, the other conditions being essentially the same, thebenzoic acid and benzaldehyde concentrations were 10.0 and 1.1 per centrespectively, corresponding to oxygen conversions of 24.2 and 1.6 percent respectively. Still higher concentrations of benzoic acidincreasing the ratio of inlet oxygen.

stated.

in the liquid have been obtained by furgler ur experiments along thisline have shown that under the conditions of these tests thebenzaldehyde concentration remains in the neighborhood of about 1 percent, irrespective of any increase in benzoic acid concentration, andaccordingly the ratio of acid to aldehyde formation may be controlled.Tests made at temperatures as low as 220 (1., using an air input of 700liters per hour, corresponding to 31.2 mol. per cent of oxygen, havegiven benzoic acid and benzaldehyde concentrations of 15.1 and 1.9 percent respectively, corresponding to oxygen conversions of 26.6 and 1.7per cent respectively.

Experiments with other types of cyclic compounds have demonstrated thewide applicability of the processes according to the invention toorganic compounds of the type For example, naphthalene may be oxidizedto produce phthalic anhydride, and oxygenated compounds may be made froma variety of other cyclic compounds, such as cyclohexane and xylene. Ourtests with commercial xylene have indicated that toluic aldehydes, acidsand anhydrides may be produced. In our investigations with compoundsother than toluene, the procedure Was essentially similar to thatdescribed hereinabove.

In most cases, the compound being treated will vaporize sufiiciently toadequately provide the desired temperature control. In some cases,however, the material may have such a low vapor pressure that adequatecontrol is not provided, or this result may arise where the material isdepleted by reaction and the products do not possess sufliciently highvapor pressures. Our invention also provides for such cases. In thisevent, a material may be added to the liquid to act as a heat-exchangingcomponent. Such a material should possess a high vapor pressure at, andits critical temperature should be above, the temperature of reaction,and it should be inert under the conditions of reaction. Likewise itshould be inert, and miscible with the material to be oxidized. For mostpurposes water is an ideal heat exchanging medium for such use, becauseit possesses a critical temperature in excess of that generallynecessary, its vapor pressure is high at elevated temperatures, and ithas a high latent heat. In most cases, some water will be formed inthese reactions, but because its concentration is normally low, itseffect will usually be of minor consequence, and water may be added tothe charge, or, in continuous processes, the water may be allowed toaccumulate to the necessary amount.

Materials of the type referred to are added solely for theirheat-exchanging properties, and they do not enter into the reaction, andconsequently are not active agents as that term is used herein. They mayalso be used as a means of intimately contacting oxygen with thecompound to be oxidized. Thus a solution of oxygen in carbontetrachloride may be mixed with the compound either in the saturator orthe two-phase procedure. In both cases it provides an intimatecommingling of the reactants, and in the saturator procedure an inertmaterial is added which modifies the intensity of the reaction by actingas a diluent, while in the procedure last descrbed, the same result isachieved by the heat-exchanging efi'ect.

So far as we are now aware, it is characteristic of our invention thatthe major portion of the oxidized products retain their aromaticcharacter, and where both aldehydic and acidic products are formed, theacidic compounds usually predominate. The ring is not broken in theoxidation, or, as in the case of polynuclear compounds, at least onering nucleus remains where the original compound was composed of severalrings. This is an important benefit of the invention, because itcontributes to the production of attractive yields of useful cycliccompounds which have hitherto been made by indirect or expensiveprocesses, or by processes which possessed various disadvantages.

The process according to the invention is simple, direct, productive ofgood yields at low cost, and renders unnecessary the use of activeagents with their attendant cost, and difiiculty of separation andrecovery. A particularly important benefit is consequent upon directoxidation combined with accurate temperature control. Not only does theinvention provide ready and accurate temperature control, but, what isof at least equal importance, it insures in large masses of reactingliquids an almost perfect uniformity of temperature with substantiallyno temperature gradient or tendency to overheating at any point.

Claims generic to the process of oxidizing mode of operation of ourinvention, and have illustrated and described what we now consider to beits best embodiment. However, we desire to have it understood that,within the scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

We claim:

1. A process of directly oxidizing a compound of the group consisting ofcyclohexane and related naphthenes, comprising contacting the compoundin a liquid body at an elevated temperature with molecular oxygen in aclosed system and under a pressure substantially in excess of the vaporpressure of the compound at said temperature, and thereby producing apartial oxidation product of the compound.

2. A process of directly oxidizing a compound of the group consisting ofcyclohexane and related naphthenes, comprising contacting the compoundin a liquid body at an elevated temperature with molecular oxygen in aclosed system and under a pressure substantially in excess of thecritical pressure of the compound at said temperature, and therebyproducing a partial oxidation product of the compound.

3. A process of directly oxidizing a compound of the group consisting ofcyclohexane and related naphthenes, comprising contacting the compoundin a liquid body at a temperature intermediate its normal boiling andcritical temperatures with molecular oxygen in a closed system and undera pressure substantially in excess of the vapor pressure of the compoundat said temperature, and thereby producing a partial oxidation productof the compound.

4. A process of directly oxidizing a compound of the group consisting ofcyclohexane and related naphthenes, comprising passing a gas containingmolecular oxygen into a liquid body of the compound heated to anelevated temperature intermediate its normal boiling and criticaltemperatures, in a closed system and under a total pressure in excess ofthe vapor pressure of the compound at reaction temperature, and whilemaintaining the compound in a liquid body at said temperature supplyingoxygen substantially at the rate at which it is consumed, and therebyproducing a partial oxidation product of-said compound.

5. A process of directly oxidizing a compound of the group consisting ofcyclohexane and related naphthenes, comprising passing a gas containingmolecular oxygen into a heated liquid body of the compound in a closedsystem, adding oxygen to replace that consumed, maintaining a totalpressure in the system substantially in excess of the vapor pressure ofthe compound at reaction temperature, regulating the pressure in thesystem to cause evaporation of liquid to maintain the entire liquid bodyuniformly at a reaction temperature intermediate the normal boiling andcritical temperatures of the compound, and condensing the vaporizedliquid in the system, and thereby producing a partial oxidation productof the compound.

6. A process according to claim 5, said pressure being in excess of thecritical pressure.

7. A two-phase liquid-vapor process of directly oxidizing cyclohexane,comprising passing an oxygen-containing gas into a liq uid body ofcyclohexane in a closed system at an elevated temperature, adding oxygento replace that consumed, maintaining a total pressure in the system inexcess of the vapor pressure of cyclohexane at said temperature, andabsorbing heat of reaction to maintain the entire liquid body uniformlyat said temperature by vaporization and condensation in the system ofthe liquid, the temperature of the liquid being determined by regulationof the pressure in the system.

8. A process of directly oxidizing cyclo- 100 hexane comprisingcontacting liquid cyclohexane with molecular oxygen in a closed sys temat a temperature intermediate the normal boiling and criticaltemperatures of cyclohexane and under a pressure substantially in 105excess of the vapor pressure of cyclohexane at said temperature.

In testimony whereof, We hereunto sign our names.

HENRY O. FORREST. 11o PER K. FROLICH.

